Mobile device display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a mobile device screen or portion thereof with a graphical user interface embodying the present design.

The broken lines showing the mobile device hardware is for the purpose of illustrating environmental structure and forms no part of the claimed design. Additionally, the broken lines showing the display screen and features of the graphical user interface illustrate portions of the article and forms no part of the claimed design. 

CLAIM The ornamental design for a mobile device display screen or portion thereof with a graphical user interface, as shown and described. 